The present invention pertains to seismic data filters and more particularly to filters to remove dc offset added to data in an analog to digital conversion.
Seismic data gathering may be done either on land or at sea. In either situation the basic process is the same. An acoustic energy source is used to generate seismic acoustic waves which travel through subterranean formations. Portions of these acoustic waves are reflected back to the surface by formation interfaces, that is, changes in density from one formation to an adjacent formation. Portions of these acoustic waves are also refracted by these interfaces, that is, travel along the interface before traveling back to the surface. Acoustic waves that are reflected or refracted back to the surface are detected by acoustic energy receivers. In some cases these may be as few as one receiver located many miles from the energy generators to detect refracted acoustic waves which travel along formation interfaces for great distances. Generally a string or line of acoustic energy receivers are laid along the ground for land surveys or towed by a marine vessel behind the acoustic energy sources for sea surveys. The line of acoustic energy receivers may be geophones, hydrophones, etc., and are spaced anywhere from seven to one hundred twenty feet apart.
Presently there exist many systems for collecting the data gathered by the line of acoustic energy detectors. However, as the number of acoustic energy detectors increases, the data gathered along with processing complexity increases accordingly. The prior art solution to increasing complexity has been to increase the size of the data processing unit or computer which records the data gathers.
Increasing the size of the processing unit does not solve many present problems and in some respects further complicates them. Many problems are emphasized by increasing the amount of data and the speed with which it is gathered. Input selection is done manually and with additional detectors, the selection is further complicated. Increased data input requires a multiplexed format which complicates transmission, reception and recordation. There is no intercommunication within the system between a compiler, such as a DFS V, unit and the processing computer, sucn as an SEL minicomputer. It is desirable to record the gathered data in a floating point format. This is presently done by software since a hardwired system to format the data in floating point does not exist in the prior art. In the accumulation of data, the time break window for arriving data is set in the hardware. This requires the setting of a window with hardwired delays in order to allow for a variable time break depending on the situation. If a change in the present window is necessitated, the hardwired circuits must be changed.
Presently seismic data is received in serial format. The data is reformatted to a parallel format for further processing. This method is relatively slow and the size of the processing computer must be increased to accept a greater amount of input data resulting from an increased number of acoustic energy detectors.
In land seismic exploration, when an acoustic energy source is moved, the traces from the end detectors must be manually cancelled from the recorded seismic data to provide continuity in comparing data from one source to the other. This is an additional requirement of man hours and a waste of recording capability.
While seismic data is being gathered, the traces from each acoustic energy detector is monitored bh an electrostatic camera. Normally if a noisy channel is suspected, an electrostatic "picture" of the trace must be taken and the input from that channel may be turned off. Unfortunately, the "picture" must be taken to be assured that a specific channel is noisy and the printing of such a record requires time. In processing, the seismic data is normally stacked and the recorded data will have the noisy data stacked with good or clean data until a decision to eliminate the noisy channel can be made.